docs: def _relative(self, uri):
          """
          if uri is relative, re-relate it to our basedir
          """
  
          if uri.startswith("http:") or \
             uri.startswith("https:") or \
             uri.startswith("file:") or \
             uri.startswith("/"):
              return uri
  
          elif exists(uri):
              return relpath(uri, self.basedir)
  
          else:
              return uri